I've used Net::Domain for this very purpose, and so far it's worked okay for me on single-interface boxes. And that's really the only time such a "Who am I?" question makes any sense, because IPs are not attached to computers but to interfaces. A computer acting as a gateway between two networks, for example, will have two interfaces and, hence, two associated IP addresses. Which one is the "computer's IP address"? Well, the question just doesn't make sense. And I don't know what Net::Domain would do in such a case, because I haven't tried it.